The invention relates to liquid crystal display and fabrication thereof, and in particular to a thin film transistor of a liquid crystal display and fabrication thereof.
Liquid crystal display (LCD) is a commonly used flat panel display. Owing to dielectric anisotropy and conductive anisotropy of liquid crystal molecules, molecular orientation of liquid crystals can be shifted under an external electronic field, such that various optical effects are produced.
A LCD panel is generally made up of two substrates, with a cell gap therebetween, and a liquid crystal layer interposed between two substrates. A plurality of electrodes is formed on the two substrates, respectively, to control the orientation and oriental shift of liquid crystal molecules.
FIG. 1 is a plane view of a conventional thin film transistor. Referring to FIG. 1, a thin film transistor controls LCD panel switch on or off, acting as a switch device. A gate electrode 102 overlaps a source electrode 106 and a drain electrode 104, such that a coupling capacitance Cgd occurs between the gate electrode 102 and the drain electrode 104. While gate electrode 102 is turned off, pixel potential would be rapidly dropped due to the coupling capacitance. This phenomenon can be named as feed-through effect.
In general, feed-through effect is more serious as coupling capacitance increases. Although feed-through effect can be reduced by increasing storage capacitor (Cst), however, aperture ratio is reduced accompany with the increase of storage capacitor (Cst). In addition, when the problems of exposure misalignment or etching unevenly raised, the coupling capacitance Cgd would generate short mura at the connections between photo masks, or flicker is generated. The problem described can be eliminated by reduced Cgd.